Trolling motor with integral sonar transducer

ABSTRACT

A trolling motor having an integral sonar transducer including: a submerged motor housing; an electric motor housed in the housing; a sonar transducer housed in the housing; a motor controller having a pulse width modulated output and a shielded electrical cable connecting the sonar transducer to a sonar device. Noise from all sources (i.e., electrical noise from ground loops, radio frequency interference, and magnetic interference) is suppressed in the output signal of the transducer through a number of techniques. The electrical cable includes an outer shield connected to the chassis ground of the trolling motor; an inner shield connected to the circuit ground of the sonar device; and a pair of signal carrying conductors comprising a twisted pair. In addition, the resonant frequency of the transducer is selected such that it is not a harmonic of the operating frequency of the pulse width modulated output of the motor controller.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from copending U.S. provisional patentapplication Ser. No. 60/218,850, filed Jul. 13, 2000, the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a trolling motor for a fishing boat.More particularly, but not by way of limitation, the present inventionrelates to a trolling motor for a fishing boat with an integral sonartransducer for use with a fish locator, depth finder, or the like.

2. Background

Trolling motors are well known in the art as are sonar devices.Generally speaking, a trolling motor is a small electric motor coupledto a propeller for quietly adjusting the position of a fishing boat atrelatively low speeds. Trolling motors are available with a variety offeatures such as variable speed, electric steering, power mounts, etc.Some models connect to a sonar device such as a depth finder to providethe user with navigational options, for example following astraight-ahead course, following a bottom contour, etc.

Sonar devices are also popular equipment for the sport fisherman.Typically, a sonar transducer is placed in the water facing generallydownward. A control unit, preferably mounted within view of thefisherman, causes the transducer to emit a pulse of acousticalultrasonic energy. Upon completion of the pulse, the control unit usesthe transducer to “listen” for return echos. By measuring the timeperiod to a particular echo, the control unit can determine the distancebetween the transducer and an object. By measuring the amplitude of theecho, the control unit may predict the size of the object. Manycontemporary control units employ complex computer software andadditional sensors to provide information to the fisherman regarding ahost of underwater factors and navigational information.

In a conventional installation, an on-board sonar device utilizes atransducer that has been mounted to the hull of the boat. This sort ofmounting arrangement, however, is not without its problems. For example,if the transducer is attached to the boat with screws, the screws mustnecessarily penetrate the outer surface of the hull at a point that maybe at least occasionally beneath the water line. Obviously, this canlead to leaks and associated problems. Alternatively, if the transduceris adhesively mounted, the adhesive must be capable of continuouscontact with water without becoming compromised. Mounting a transducerto a bracket which is attached to the boat above the waterline canmitigate these concerns to a certain extent, but that solution is notalways available.

Since a trolling motor must also be mounted to the boat and since themotor and propeller must be submerged, it would thus appear, at least atfirst blush, that a trolling motor would provide an ideal platform forplacement of an ultrasonic transducer. The prospect of placing a sonartransducer in a trolling motor is even more appealing in light of thefact that, at least with high-end equipment, an ever increasing numberof trolling motor features are being coupled to display devices such assonar control units so that an operator may be provided a visualindication of operating parameters and conditions. Placing a sonartransducer in a trolling motor also simplifies cable routing since thesonar cable may easily be routed through the trolling motor supportcolumn.

Unfortunately, prior attempts to locate a sonar transducer in a trollingmotor have been hindered by the amount of electrical and electromagneticnoise present in the general vicinity of the trolling motor. Trollingmotors generate such noise in at least four areas.

First, by the very nature of the control system that is typically usedin combination with a trolling motor. Electronic control of trollingmotors and electronic steering systems have almost universally employedpulse width modulation (PWM) schemes, as opposed to linear drivecircuitry. PWM control systems operate more efficiently than linearsystems which result in components that operate at a substantially lowertemperature, utilize less power, and need less complex drive circuitry.However, the general nature of a PWM control system requires productionof a substantially rectangular waveform at the output of the driver.Such a waveform inherently contains substantial harmonic content manytimes over the fundamental frequency of the PWM signal. When a PWMsignal is used to drive the motor, the electrical currents arerelatively high, thus generating nontrivial amounts of high frequencyelectrical and electromagnetic noise. If this signal has harmoniccontent approximately equal to the frequency of the signal produced bythe sonar transducer, the received transducer signal may be completelyobscured by the noise thus produced. Further, if the transducer cableand the power supply cable for the motor both run through the supportcolumn, the opportunity for cross talk from the power cable to thetransducer cable is greatly enhanced. Of course, such cross talk posesstill another opportunity for the motor drive signal to find its wayinto the received sonar signal.

Second, noise generally referred to as “brush noise” is created by themotor. As the armature rotates in the motor, the brushes ride on thecommutator, cyclically energizing the windings located on the armature.As a particular winding is de-energized during this process, arcing islikely to occur between the brush and the contact on the commutatorresulting in electric and electromagnetic noise.

Third, substantial amounts of noise may also be introduced into thereceived sonar signal through common circuit conductors. Commonly knownas ground loops, unwanted electrical currents often flow throughconductors when multiple electrical paths are created through theinterconnection of multiple circuit elements, e.g., the trolling motorand the sonar control unit. For example, the control unit may beconnected to the boat's electrical system, the negative lead of which isnormally connected to chassis ground. The trolling motor may beconnected instead to a spare battery located in the boat. The negativepower supply lead from the spare battery may also be connected totrolling motor chassis components. Once the trolling motor is mounted tothe boat, or when placed in the water, an electrical connection is madebetween the boat electrical system and the trolling motor electricalsystem. In this case, no currents will flow because there is a singlecommon connection. On the other hand, if, for example, a shield within asignal cable is then connected between the trolling motor and thecontrol unit, unwanted electrical current will likely flow when eitheran accessories attached on the boat is powered, or when the trollingmotor is operational. The resistance of the conductors causes voltagelosses when such currents flow which appear as noise to the receivercircuitry. The reactive characteristics of the conductors will likewiseinduce noise from these currents.

Finally, the spinning armature in the motor produces an externalmagnetic field which varies over time at a frequency proportional to therate of rotation of the motor. This varying magnetic field will induce avoltage in nearby conductors. The wires connected to a sonar transducermounted in a trolling motor will necessarily be subjected to such amagnetic field which will result in additional unwanted noise in thereceived sonar signal.

The ability of an electronic device to resolve meaningful informationfrom a received signal is determined, in part, by the signal to noiseratio (often given in dB) present at a receiver. Thus, as is well knownto those skilled in the art, placing the sonar transducer near thetrolling motor will cause the introduction of a substantial degree ofnoise into the receiver both from noise resulting from the motor driveand possibly from ground loops, thereby reducing the circuit's abilityto resolve meaningful information from a received pulse.

Trolling motor models are available which include an integral sonartransducer. However, these trolling motors and the integral sensor onlyoperate with a specific control unit which is properly configured forsuch operation. These systems are designed such that electrical noisethat is created by the drive circuitry for the trolling motor and noiseinduced from ground loops will appear as common mode noise relative tothe transducer output and may be subtracted out of the sonar signal bythe receiver circuitry. The circuitry incorporated into the vastmajority of trolling motors which are currently available does not allowfor this sort of solution. An example of such a combination is disclosedin U.S. Pat. No. 5,525,081 issued to Mardesich, et al. which is herebyincorporated by reference.

It is thus an object of the present invention to provide a trollingmotor with integral sonar transducer which will operate with an existingsonar control unit. It is also a related object of the present inventionto provide a trolling motor with integral sonar transducer wherein thereis substantial improvement in the signal to noise ratio of the signalpresented to the sonar receiver from the transducer so incorporated intothe trolling motor.

It is a further object of the present invention to provide a cable forconnection between a sonar transducer and a sonar control unit whichprovides improved shielding from sources of high frequency noise inclose proximity to the cable.

It is yet another object of the present invention to provide a methodfor electrically connecting a trolling motor with integral sonartransducer to a power source and to a sonar control unit so as toeliminate multiple ground paths on the sonar signal or reduce the effectthereof.

SUMMARY OF THE INVENTION

The present invention provides a trolling motor for a fishing boat withan integral sonar transducer for connection to a sonar control unit. Inone embodiment of the present invention, an inventive cable forconnecting the sonar transducer to a control head provides improvedshielding from unwanted noise emanating from nearby sources.

In yet another embodiment of the present invention, there is provided amethod for connecting the trolling motor to an electrical system and thesonar control unit to the transducer which will avoid the creation ofground loops.

Further objects, features, and advantages of the present invention willbe apparent to those skilled in the art upon examining the accompanyingdrawings and upon reading the following description of the preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the inventive trolling motor with integral sonar transducerin its general environment.

FIG. 2 provides a side view of the inventive trolling motor withintegral sonar transducer.

FIG. 3 provides a cutaway side view of the inventive trolling motor withintegral sonar transducer.

FIG. 4 provides a representative wiring diagram for connection of theinventive trolling motor to a power supply and for connecting theintegral sonar transducer to a sonar control unit.

FIG. 5 provides a block diagram of a typical controller for a trollingmotor which provides pulse width modulated drive signals.

FIG. 6 provides a detail view of a stripped end of a sonar transducercable incorporated in the inventive trolling motor with integral sonartransducer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the inventive trolling motor with integralsonar transducer 10 is shown in its general environment in FIG. 1.Typically, trolling motor 10 is removably attached to a fishing boat 18.To fully utilize the inventive aspects of trolling motor 10, boat 18 ismost preferably equipped with sonar control unit 28. In operation,trolling motor 10 is preferably controlled by foot pedal 24 connected totrolling motor 10 by control cable 22. Sonar transducer 30 incorporatedin trolling motor 10 is connected to sonar control unit 28 with cable32.

Referring next to FIGS. 2 and 3, trolling motor 10 preferably comprises:motor housing 14 containing motor 34 which is drivingly coupled topropeller 12; support column 16 supporting motor housing 14 frommounting bracket 20; control head 26 mounted to the upper end of supportcolumn 16 housing motor controller 42 (FIG. 5); and cables 22 and 32(FIG. 1) passing through support column 16 thereby reducing exposure towater.

Sonar transducer 30 is mounted to trolling motor 10 with shield 40 toprotect transducer 30 from electromagnetic fields produced by motor 34.Cable 32 preferably contains a pair of twisted conductors 44 a and 44 b(FIGS. 4 and 6) which connect transducer 30 to sonar control unit 28.

Referring next to FIG. 6, wherein is shown the construction of cable 32,conductors 44 a and 44 b are housed within an inner dielectric jacket46. Inner jacket 46 is next surrounded by in inner shield 48.Preferably, inner shield 48 is a metal foil, however, it will beapparent to one skilled in the art that braided shield may also performsatisfactorily with the present invention. Shield 48 is then surroundedby an intermediate dielectric jacket 50 which is next wrapped in outershield 52. Preferably, outer shield 52 is likewise metal foil, howeveronce again, braided shield may also perform with acceptable results.Finally, outer jacket 54 surrounds and protects outer shield 52. Itshould be noted that shielded cable with twisted pair signal conductorsis known in the art. However, unlike prior art cable used with sonardevices, the inventive cable provides a second layer of shielding 52separated from inner shield 48 by tubular dielectric 50. As shown inFIG. 4 and discussed further hereinbelow, inner shield 48, asincorporated in the inventive trolling motor, is referenced to circuitground 100 (FIG. 4) of sonar control unit 28 while outer shield 52 isreferenced to the negative lead 104 of trolling motor power supply 106.

A cable constructed in accordance with the present invention will reducethe effects of nearby motor-produced magnetic fields on the receivedsonar signal. As is known in the art, a varying magnetic field willinduce a voltage in nearby conductors. In the inventive cable however,outer shield 50 shields the inner conductors from such magnetic fields.Since outer shield 50 is preferably connected at only one point,voltages induced in outer shield 50 will not result in any unwantedelectrical currents and will not affect the received sonar signal. Inaddition, the effects of any magnetic field which does in fact reachconductors 44 a and 44 b will be minimized by the twisting of conductors44 a and 44 b in cable 32. In a similar manner, the outer shield 50 willshield signal carrying conductors 44 a and 44 b from the effects ofelectrical noise (i.e., radio frequency interference, crosstalk fromadjacent conductors, and the like), of particular importance isprotection from the noise produced in driving the motor with a pulsewidth modulated signal. Again, the twisting of conductors 44 a and 44 bwill also reduce the effects of such noise.

Referring to FIG. 6, a motor controller 42 for use with the inventivetrolling motor 10 would typically include pulse width modulator 62,reversing relay 60 energized by relay driver 64, motor driver 66protected by freewheeling diode 74, and current sense circuitry 68 whichconditions the output of current sense resistor 70. Preferably, pulsewidth modulator 62 is implemented using a microcontroller 72. However,it will be apparent to those skilled in the art that pulse widthmodulation may be accomplished by any one of a variety of known methodsfor performing such modulation. In operation, the controller receives aspeed command from an user operated input device, preferably a footpedal 24. The controller then calculates a duty cycle corresponding tothe commanded motor speed and provides motor driver 66 with theappropriate waveform.

As previously discussed, the waveform produced by a PWM controller istypically rectangular in nature and thus a substantial amount of energyis produced at harmonic frequencies of the PWM waveform. An RC networkcomprising resistors 74 and 76, and capacitor 78 provides low passfiltering of the waveform driving motor driver 66. This filtering tendsto somewhat “round” the waveform driving the motor and thus reduces theharmonic content of the signal so produced. As will be apparent to oneskilled in the art, this increases the switching time of driver 66thereby increasing the power dissipated in driver 66. Hence it can beseen that a tradeoff exists between the efficiency of the motor driverand reduced high frequency noise produced by the driver. For example, itwas discovered that selecting a value of ten ohms for resistor 74, avalue of fifteen ohms for resistor 76, and a value of 0.01 microfaradsfor capacitor 78 produced a noticeable reduction in harmonic noise witha minimal increase in the power dissipated in driver 66.

Generally speaking, a sonar transducer of the type incorporated in thepresent invention will preferably have a resonant frequency whichcoincides with the frequency at which the transducer is intended tooperate. In the preferred embodiment, sonar transducer 30 is intended tooperate at approximately 200 kilohertz. It will be apparent to oneskilled in the art that such transducers are available for operation ata number of different frequencies and the selection of a particularfrequency is not critical for operation of the present invention.

According to a preferred aspect of the instant embodiment, the frequencyof the pulse width modulator 62 is selected such that the resonantfrequency of the transducer 30 is not an exact harmonic of the pulsewidth modulation frequency, thereby minimizing or preventing directexcitation of sonar transducer 30 by the motor controller 42 or themotor 34. It should be noted that at particular frequencies, a typicalsonar transducer will exhibit a relatively low impedance. Accordingly,it is even more preferable to “tune” the pulse width modulationfrequency to a particular transducer, or select a transducer for aparticular pulse width modulation frequency, such that the transducercrystal will exhibit a low impedance at the frequency of the pulse widthmodulation thereby effectively shunting any signal induced into thereceived sonar signal by the motor circuit.

It will be further apparent to one skilled in the art that, except as tofrequency as discussed hereinbefore, operation of the motor controlleris not a part of the present invention. Accordingly the discussion ofthe motor controller in reference to the preferred embodiment is givenonly by way of example and not limitation.

Referring next to FIG. 4, interconnection between the various componentsis constrained to a large degree by the existing interface to the sonarcontrol unit 28. Typically, the sonar control unit 28 will receive powerfrom the boat's primary electrical system. Therefore, the signal fromthe sonar transducer 30 will ultimately be referenced to chassis groundof the boat. It should also be noted that in a typical configuration,one lead connected to transducer 30 is also connected to circuit groundwithin control unit 28 and thus, conductor 44 b of cable 32 connects thetransducer 30 to circuit ground at sonar control unit 28. The otherconductors of cable 32 are preferably connected as follows: twisted pairconductor 44 a provides the signal path to and from transducer 30; innershield 48 is connected to the negative lead 100 of the boat's electricalpower supply 102 at sonar control unit 28 (circuit ground) andpreferably to shield 40 (FIGS. 2, 3, and 4) over transducer 30 at motorhousing 14 (FIGS. 2, 3, and 4); and preferably, outer shield 50 isconnects to the negative power supply lead 104 of the trolling motorpower supply 106 at control head 26. Optionally, conductor 44 b is alsoconnected to inner shield 48 at both control unit 28 and at transducer30.

It should be noted that it is common in the art to switch the negativeside of the trolling motor with motor driver 66 (FIG. 4). In addition,reversing relay 60 reverses the polarity of the conductors which supplypower to the motor. As a result, when trolling motor 10 is connected toa battery independent of the boat's electrical system, there is not achassis ground, as such, connected to the motor. In fact, there may notbe a continuous connection of the negative lead 104 of the trollingmotor power supply 106 to the motor 34 or the chassis. Optionally thesupport column 16 may be connected to the negative power supply lead 104of trolling motor battery 106 thereby providing a chassis groundrelative to the trolling motor power supply 106.

Preferably, the trolling motor controller 42 derives its primary powerfrom an external battery independent of the electrical system of theboat. Hence, a fisherman will not have to worry about retainingsufficient charge in the boat's battery to restart the boat's engine. Ifthe external components of the trolling motor are not connected to thenegative power supply of the battery, inner shield 48 comprises a singleground point between the two electrical systems at the transducer shield40. On the other hand, if support column 16 is connected to the negativepower supply lead for the trolling motor 10, there will exist thepotential for two common ground connections between the two electricalsystems, the second one being through the support components of thetrolling motor. While such a connection may result in some unwantedelectrical current flowing through inner shield 48, since motor 34 doesnot draw power through a chassis ground, no trolling motor currents willflow through inner shield 48 or conductor 44 b and therefore, the impacton the received sonar signal will be minimal.

As will be understood by those skilled in the art, although the abovepreferred embodiment of the inventive apparatus has been discussed inregard two independent electrical systems, the inventive apparatus wouldperform acceptably when operated from a single power supply common toboth the trolling motor 10 and sonar control unit 28.

It should be noted that while it may be possible to obtain an acceptablesignal to noise ratio with either the cable disclosed herein orappropriate matching of the pulse width modulation frequency and thetransducer, preferably a trolling motor constructed in accordance withthe present invention would incorporate both the cable and matching ofthe pulse width modulation frequency and the sonar transducer.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned above as well as those inherenttherein. While presently preferred embodiments have been described forpurposes of this disclosure, numerous changes and modifications will beapparent to those skilled in the art. Such changes and modifications areencompassed within the spirit of this invention as defined by theappended claims.

What is claimed is:
 1. A trolling motor comprising a submerged motorhousing; a sonar transducer housed in said motor housing, saidtransducer having a transducer output; and an electrical cable connectedto said transducer output comprising: a pair of conductors connected tosaid transducer output, said pair of conductors twisted about eachother; an inner conductive shield surrounding said pair of conductors; adielectric jacket surrounding said inner conductive shield; and an outerconductive shield surrounding said jacket.
 2. The trolling motor ofclaim 1 further comprising: a motor housed in said motor housing; and amotor controller having a pulse width modulated output to provideelectrical power to said motor, wherein said sonar transducer has aresonant frequency, and said pulse width modulated output operates at anoutput frequency, and wherein said resonant frequency is not a harmonicof said output frequency.
 3. The trolling motor of claim 2 wherein saidsonar transducer will exhibit a low impedance at a shunting frequencyand wherein said shunting frequency is a harmonic of said outputfrequency.
 4. A trolling motor comprising: a submerged motor housing; amotor housed in said motor housing; a sonar transducer housed in saidmotor housing, and having a transducer output said transducer having aresonant frequency; an electrical cable connected to said transduceroutput, wherein said cable includes an inner conductive shieldsurrounding a twisted pair of conductors, a dielectric jacketsurrounding said inner conductive shield, and an outer conductive shieldsurrounding said dielectric jacket and a motor controller having a pulsewidth modulated output to provide electrical power to said motor, saidoutput operating at an operating frequency, wherein said resonantfrequency is not a harmonic of said operating frequency.